This invention relates to optical glass which is light in weight, high in transparency, low in dispersion and relatively high in refractive index, and in particular to optical glass comprising a four-indispensable component system of SiO.sub.2 --Li.sub.2 O--K.sub.2 O--TiO.sub.2.
Optical glass having a refractive index (n.sub.d) of 1.523 and a specific gravity of 2.52 is used for ordinary spectacle lenses. However, spectacle wearers who require their spectacles to be light in weight are gradually increasing. Light-weight plastic lenses are being used instead of glass lenses, but plastic lenses have a disadvantage in that they are easily damaged and thus, the demand for glass lenses is still high. Recently, a spectacle lens having as high a refractive index as about 1.70 has been developed (see U.S. Pat. No. 4,084,978) and has been attracting attention, but this lens has been unsatisfactory from the viewpoint of reduced weight although it has an advantage in that because of its high refractive index, it may be thin even if it is high in refractive power. Conventional high refractive index lenses have a specific gravity of about 3.0 and are very heavy as compared with conventional glass lenses (having a specific gravity of 2.52). Although high refractive index lenses can be made thin, the weight of the entire lens is not reduced much and sometimes it is somewhat increased. In addition, these high refractive index lenses cannot be said to be sufficiently high in transparency and they are generally high in dispersion performance and create great chromatic aberration, which has led to a disadvantage in use in that a rainbow is seen in the lenses.